The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for vibrational and acoustic dampening of the actuator assembly in a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
A continuous goal in the manufacture of disc drives is to design a disc drive with higher data capacity. Currently, the data capacity of disc drives across the industry grows at approximately sixty percent per year. One way to increase the capacity of a disc drive is to increase the track density on the recording surface of the disc. The data is stored on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. By packing the tracks more closely together, more data can be stored on the disc. One constraint that prevents designs with more closely spaced tracks is the fact that the actuator assembly has a resonant frequency or moves in a direction transverse to the track during track following operations. Since the track must be followed in order to read data from the disc surface, the track must be wide enough so that the transducer remains positioned over a track. A device that reduces vibration allows for more closely spaced tracks. One source of transverse movement in a bearing cartridge occurs from imperfections in the ball bearings as they roll against the ball bearing raceways.
Another problem associated with current actuators includes high settle times. At certain times, a seek is performed to move the transducer attached to the free end of the actuator assembly from a first track to a second track. During seeks where multiple tracks are crossed, the actuator follows a velocity profile. At the end of the seek, the actuator is stopped and actually settles over the target track where the next data to be read is stored. In many disc drives, the actuator xe2x80x9cringsxe2x80x9d or vibrates across the track. The data can not be accessed until the actuator settles down or the ringing slows. This results in increased access time. Decreasing the access time is another constant goal in disc drive design.
What is needed is an actuator assembly that has improved settling characteristics after a seek from a first track on the disc to a target track on the disc. What is further needed is an actuator assembly with minimized vibration during track following operations of the disc drive. In other words, there is a need for an actuator assembly that has improved vibration characteristics while under any type of servo control. What is also needed is a device that will accommodate thermal mismatches that might occur between the bearing cartridge and the E-block as the disc drive heats from a starting temperature to an operating temperature. In addition, there is a need for an actuator assembly that results in reduced damage to assembled components of the actuator assembly as a result of a shock event. Still a further need is an actuator assembly with reduced acoustical noise related to rotating bearings. Also needed is a device that can be assembled using current assembly techniques.
A disc drive, includes a base, a disc stack rotatably attached to the base, and an actuator assembly movably attached to the base. Attached to one end of the actuator assembly is one or more transducers. The actuator assembly includes arms on one end for holding the one or more transducers and a portion of a voice coil motor on the other end of the actuator assembly. The voice coil motor moves the actuator assembly and the transducers attached thereto to various locations over the disc where data is located. The actuator assembly has an opening therein. A bearing cartridge is attached to the opening in the actuator assembly. A tolerance ring is used to attach the bearing cartridge to the opening in the actuator assembly. The tolerance ring includes a layer of viscoelastic material. The viscoelastic material is sandwiched between the first layer of metallic material and the second layer of metallic material. The tolerance ring is a plurality of ridges formed about the periphery of the tolerance ring. The ridges may be formed in an arcuate shape or having an arcuate cross section. The tolerance ring is dimensioned so that attachment of the bearing cartridge and tolerance ring to the actuator assembly requires a press fit. The dimensions of the tolerance ring are selected so that the natural frequency of the actuator assembly is not matched to the natural frequency of the tolerance ring.
Advantageously, the method and apparatus described for attaching the bearing cartridge and the E-block or comb to form the actuator assembly has improved settling characteristics after a track to track. Vibration in the actuator assembly is minimized during track following operations of the disc drive. The actuator assembly has improved vibration characteristics while under any type of servo control. The actuator assembly also accommodates thermal mismatches that might occur between the bearing cartridge and the E-block as the disc drive heats from a starting temperature to an operating temperature. The tolerance ring also absorbs vibrations resulting from imperfections in the bearings as they roll within the race of the bearing set within the bearing cartridge. Still another advantage is reduced damage to assembled components of the actuator assembly as a result of a shock event. The actuator assembly with the tolerance ring including the damping material has reduced acoustical noise related to the rotating bearings. The actuator assembly can also be assembled using current assembly techniques.